1. Field of the Invention
The present invention relates to a bismuth ferrite perovskite oxide and an oxide composition/oxide body/piezoelectric device/liquid discharge apparatus using the same.
2. Description of the Related Art
Provskite oxides having ferroelectricity are used in various applications, such as piezoelectric devices, switching devices, and the like. For example, as a perovskite oxide having excellent piezoelectric properties, lead zirconate titanate (PZT) is known. PZT is a ferroelectric body having spontaneous polarization in the absence of electric field, and said to show high piezoelectricity at and near a morphotropic phase boundary (MPB). If environmental burden is considered, it is preferable that Pb content is reduced as much as possible and a non-lead system that does not include Pb is more preferable. In non-lead perovskite oxides, development of new materials having high piezoelectricity has been in progress.
As a non-lead perovskite oxide having high piezoelectricity (ferroelectricity) in theory, Bi perovskite oxides have been under study. Most of the Bi perovskite oxides, however, hardly, and some of them can not, take a perovskite structure by high-temperature sintering under normal pressure.
Currently, BiFeO3 is the only Bi perovskite oxide, in bulk ceramics, that can be manufactured into a Bi perovskite oxide under normal pressure. Thus, BiFeO3 can also be easily made into a Bi perovskite oxide in thin films. As having a high Curie temperature and a large spontaneous polarization, BiFeO3 has been studied as a prospective material of dielectric memories and piezoelectric actuators. But, BiFeO3 has a low dielectric constant and a high coercive electric field Ec in addition to leakage, so that a high piezoelectric constant can not be expected from BiFeO3 alone.
Consequently, a perovskite oxide film made of a material provided by solid solving BiFeO3 into barium titanate (BaTiO3), which is known as a non-lead perovskite oxide, is disclosed in U.S. Pat. No. 7,586,234. In addition, U.S. Patent Application Publication No. 2009243438 discloses a perovskite oxide film made of a material provided by adding and solid solving Mn to B-site of BiFeO3 and Zr to B-site of BaTiO3 in the same composition as that described in U.S. Pat. No. 7,586,234 in order to improve leakage characteristics due to low insulating properties of BiFeO3.
A literature by J. S. Kim et al., Journal of Applied Physics, Vol. 96, No. 1, pp. 468-473, 2004, describes that in a solid solution of BiFeO3—ReFeO3—BaTiO3 (Re is Dy, Pr, or La), ferroelectricity and ferromagnetism may coexist due to oxygen loss in BiFeO3 and spontaneous magnetization of ReFeO3.
A literature by Rai et al., Material Chemistry and Physics, 119, pp. 539-545, 2010, discloses a Gd doped BiFeO3—BaTiO3 perovskite oxide in which Gd element is added to A-site of BiFeO3.
But, none of U.S. Patent Application Publication No. 2009243438, the literature by J. S. Kim et al., and the literature by Rai et al. provides satisfactory piezoelectricity.
The present invention has been developed in view of the circumstances described above and it is an object of the present invention to provide a novel non-lead perovskite oxide which can be manufactured easily and has excellent ferroelectricity (piezoelectricity).